AC motors are widely used as drive elements in systems, controlling the operation of the system by controlling the AC motor. Using an escalator as an example, it uses an AC motor as the drive motor, thereby driving escalator operation, wherein the operating speed of the stairs is influenced by the motor. Differentiated by motor control, escalators can be divided into working frequency escalators, full frequency conversion escalators, and bypass frequency conversion escalators. Here, bypass frequency conversion escalators are becoming increasingly accepted by users due to their advantages in terms of comfort and safety.
Using a bypass frequency conversion escalator as an example, it uses a bypass frequency conversion control system to drive and control the motor. When the motor is running, there is the problem of power supply switching. For example, in the start-up phase, a voltage signal output by a frequency converter is used to power and control the motor in linear acceleration to the normal speed; upon entering the normal operation phase (usually, this is operation at a basically constant normal speed), it is necessary to switch to using a network voltage signal to power and control the motor in normal speed operation. To achieve smooth switching, usually, a synchronizer will be set up in the bypass frequency conversion control system. This synchronizer can conduct sampling of the voltage signal output by the frequency converter and the network voltage signal, and monitor the synchronism between their frequencies and phases, until synchronism requirements are met, at which point the synchronizer issues an instruction to conduct switching, thereby achieving smooth switching and reducing the surge current, for a small shock produced by the escalator during this switching process.